Miners found giant gypsum crystals in the Cave of Crystals in Naica, Mexico.

In one of the largest lead and silver mines in the world, workers discovered what researchers are calling the “cathedral” of giant gypsum crystals about 300 meters (about 1,000 feet) belowground. The Naica mine in Mexico contains “huge crystalline beams,” with moonlight luster that is “unforgettable,” says Juan Manuel García-Ruiz, a crystallographer at the Universidad de Granada in Spain.

The giant, faceted crystals of gypsum — a soft, whitish mineral — are as long as 11 meters (36 feet) and up to 1 meter (about 3 feet) thick. To figure out how the crystals grew so large, García-Ruiz and colleagues studied tiny bubbles of fluids that were trapped in the crystals while they were growing.

The researchers found that the perfect balance of temperature and salinity of the waters from which the crystals grew spurred the massive crystal growth. If temperatures were much cooler, millions of small crystals of gypsum would have formed instead, and if temperatures were much warmer, a different mineral would have formed, the researchers reported in the April issue of Geology.

These crystals can continue to bloom if conditions are right, García-Ruiz says. Currently, the crystals are no longer growing because the water that feeds them is being pumped out of the cave to allow mining and exploration. If the water were allowed to run naturally through the system, however, the crystals would likely keep on growing.

Although large gypsum crystals have been found in other locations, such as near Segobriga, Spain, and in the Cave of Swords in Chihuahua, Mexico, near the Cave of Crystals, says García-Ruiz, they are unrivaled and should be preserved. These colossal crystals, he says, are “every crystallographer’s dream.”